In the past 2 years we have cloned a number of abundant cDNAs from the corneal epithelial cells of the mouse. Some of these encode metabolic enzymes, suggesting that enzymes may act as crystallins in the transparent corneas as they do in the lens. Indeed we have found that different species accumulate different enzymes in their corneal epithelial cells, reminiscent of the taxon specificity observed for enzyme-crystallins of the lens. Aldehyde dehydrogenase (ALDH) class III is the major protein in the corneal epithelial cells of mammals. We have employed the RACE technique to clone the 5' end of the ALDH class 3 corneal mRNA, identified the sequences that should constitute the 5' exon of the gene, and cloned the ALDH class 3 gene in an 18 kbp genomic fragment. This fragment is undergoing analysis.